10 June 2017

This system has been copied on 9 different simultaneous channels from
~6200 to ~6400 KHz on USB during 9 June morning. The analysis reveals it's a STANAG-4539 modem
(frame length is 287 PSK-8 symbols) running at different data signaling
rates at constant 2400Bd data rate. The system uses bursts and (possibly) ARQ
mode. My friend KarapuZ too copied this system but on a different HF segment.

Fig. 1

Fig. 2

The decisive contribution for the identification of the signal came from my friend ANgazu: he suggested that these transmissions could be the Thales HFXL modem, since they use up
to 16 narrowband channels in 200 Khz bw just using 4539 waveforms. Most likely, the heard transmissions are tests related to the Thales /French MOD contract: PEA "SALAMANDRE".

they uses an evolution from the SANAG-4539 frame structure, mainly differing in the preamble parts as shown in Figure 3

Fig. 3

Other than the long miniproble (32 symbols length rather than 31), they added a third 124 PSK-8 symbols part (termed "Extended") to the S-4539 initial synchronization preamble. The data block length (256 symbols) and the mini probe length (31 symbols) remain unchanged so that the period counts 287 symbols as in S-4539 (Figure 2).The extended synchronization preamble is specific to HF XL. This part, not included when operating according to S-4539 or MS 188-110C ISB modes, is combined with the main preamble to carry all information necessary to the HF XL waveform, in particular information on modulation choice for each channel. Furthermore, a specific redundancy capability is introduced, that ensures resilience to the loss of a channel as long as the number of channels is greater or equal to 3.

A deeper look at the preamble of one heard transmission confirms the Thales HF XL modem, as depicted in Figures 4,5

Fig. 4 - the whole preamble

Fig. 5 - the 124 symbols (51.6 msec) added by Thales

As further confirm, ANgazu measured the parts of the preamble (Fig. 6) and time durations fit perfectly:

Expanding on the high performance of the serial tone modem technology standardized in STANAG 4539 for 3 kHz sideband to conjugate a plurality of channels in a multi narrow band (MNB) waveform, this approach can be seen as an extension of the US MIL-STD-188-110C appendix F “ISB”, with the addition of specific redundancy capabilities to provide resistance to the highly variable HF channel conditions. As illustrated in Figure 7, these channels do not need to be contiguous, which allows to select only good quality and authorized channels. A 4G ALE alternate proposte ? (continue inthis post)